1. Field of the Invention
The present invention relates to a test apparatus (equipment) and particularly to a technique for testing a DUT (Device Under Test) that transmits and receives a differential signal.
2. Description of the Related Art
A differential signal is used so as to transmit and receive signals to and from semiconductor devices. For example, in XDR-DRAM (extreme Data Rate Dynamic Random Access Memory), a differential signal is transmitted bidirectionally at high speed by using a single differential transmission line. In the case where a test is performed on a device having such bidirectional differential interface, the amplitude of a differential signal output from a DUT (Device Under Test) is measured and the quality check is performed.
A test apparatus for examining a DUT having a bidirectional differential interface is studied. A transmitter and a receiver, both connected to a common differential transmission line pair (hereinafter, also simply referred to as a differential transmission line), are provided in the test apparatus. The transmitter transmits a test pattern to the DUT, and the receiver determines the logical value of a differential signal pair (hereinafter, also simply referred to as a differential signal) output from the DUT or examines the amplitudes of the differential voltage of the differential signal pair.
The receiver of the test apparatus is connected not only to the DUT via the differential transmission line pair but also to the transmitter on the test apparatus side. Therefore, the test apparatus for DUT provided with the bidirectional differential interface needs to be designed in consideration of not being affected by the output signal of the transmitter adjacent to the receiver. Related techniques are described in patent documents 1 through 3. In particular, patent document 1 discloses a circuit (hybrid circuit) that cancels the own transmission signals and receives only the signals from the other side in bidirectional communication.    [Patent document 1] Japanese Patent Application Laid Open No. S47-11702    [Patent document 2] Japanese Patent Application Laid Open No. H8-23354    [Patent document 3] Japanese Patent Application Laid Open No. 2006-23233